Tap changing transformer having means to change tap range



Oct. 24, 1967 G. R. MATHES 3,349,320

TAP CHANGING TRANSFORMER HAVING MEANS TO CHANGE TAP RANGE Filed April 1, 1965 E :s Sheets-Sheet 1 l 7 VOLTAGE r SENSITIVE ACTUATING 5/ MEANS m h INVENTOTQ GENE R. MATHES ATTORNEY G. R. MATHES Oct. 24, 1967 'TAP CHANGING TRANSFORMER HAVING MEANS TO CHANGE TAP RANGE 3 Sheets-Sheet 2 Filed April 1, i965 INVE NTOR GENE R. MATHES BY W AT TORNE Y Oct. 24, 1967 e. R. MATHES 3,349,320

AP CHANGING TRANSFORMER HAVING MEANS TO CHANGE TAP RANGE Filed April 1, 1965 I s Sheets-Sheet a /4 5 I ii 1M 1/ WWW INVENTOR I GENE R.MATHES ATTORNEY United States Patent 3,349,320 TAP CHANGING TRANSFORMER HAVING MEANS TO CHANGE TAP RANGE Gene R. Mathes, Zanesville, Ohio, assignor to McGraw- Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Apr. 1, 1965, Ser. No. 444,644 19 Claims. (Cl. 323-43.5)

This invention relates to electrical transformers and, in particular, to distribution transformers having tap changers.

Electrical transformers are often provided with tap changing means for Varying this voltage on the power system by increasing or decreasing the number of active turns in one winding with respect to another. In distribution transformers provided with tap changing means, the tap changer is conventionally of the manually operated, offload type which can only be operated to change the transformation ratio after the transformer is de-energized by removing the hand hole cover and reaching into the transformer casing. Conventional distribution transformers provided with such off-load tap changers have no means to vary the tap range and usually permit changing taps over only a fixed range, for example, in four 2 /2 percent voltage steps over a ten percent voltage range between 90 percent and 100 percent of the rated primary voltage. US. Patent 3,167,703 entitled, Self-Regulating Transformer, which issued to Carl Schindler on Jan. 26, 1965 and has the same assignee as the subject invention, discloses a self-regulating distribution transformer with an on-load tap changer which automatically changes taps to maintain the power line voltage constant, but this selfregulating transformer is also only capable of changing taps over a fixed range, and the ranges of primary voltage can only be varied by removing the transformer cover and changing connections internally of the transformer.

It is an object of the invention to provide a tap chang ing distribution transformer having means Operable from the exterior of the transformer casing for varying the primary voltage range over which the tap changer opcrates.

It is an object of the preferred embodiment of the invention to provide a self-regulating distribution transformer having an on-load tap changer capable of maintaining constant voltage on the power system and also of maintaining circuit continuity while changing taps and having means for selectively varying the primary voltage range over which the tap changer operates in a plurality of steps.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic circuit diagram of a distribution transformer embodying the invention; and

FIGS. 2 through 5 illustrate alternative embodiments of the switch means for varying the number of effective turns of the transformer primary winding and thus the voltage range over which the tap changer operates.

The invention is particularly adapted for use, and will be described in connection, with a self-regulating distribution transformer having a tap changer adapted to change taps under load and automatically maintain constant voltage on the power system of the type described in the aforementioned US. Patent No. 3,167,703 to Schindler and Us. Patent No. 3,106,675 to Riebs et a1. entitled, Electronic Voltage Regulator With Reversible Electroresponsive Operator Means, which issued on Oct. 8, 1963 and has the same assignee as the subject invention. Reference is made to the Schindler patent for details of the transformer casing, the transformer core and coil assembly, the on-load tap changer, and the voltage responsive means for actuating the tap changer to maintain constant voltage on the power system. However, the invention is also applicable to a transformer having a manually operated on-load tap changer of the type disclosed in FIGS. 19 and 20 of the aforesaid Schindler patent having means accessible from the exterior of the casing for manually operating the tap changer.

The transformer primary winding 10 surrounds a magnetic core 11 disposed within a transformer casing 12 and is inductively linked with a secondary winding 13. The primary winding 10 of the embodiment illustrated in FIG. 1 has four separate winding sections 14, 15, 16 and 17 insulated from each other. Preferably each winding section 14 and 15 is untapped and constitutes fifty percent of the transformer primary winding 10. Winding sections 16 and 17 may each be a five percent winding and have a mid-tap 21 and end taps 20 and 22 to permit an on-load tap changer 24 to vary the primary voltage over a ten percent range in four 2 /2 percent steps. Tap changer 24 is described in detail in the aforementioned Schindler patent and includes six stationary contacts 1-6 arranged in a circle; an arcuate conductive movable contact 25 adapted to bridge between adjacent pairs of stationary contacts 16; leading and trailing conductive auxiliary contact members 27 and 28 disposed at positions circumferentially removed from the leading and trailing edges of arcuate movable contact 25 and spaced apart approximately the same angle as alternate ones of the stationary contacts 1-6; and resistors 29 connected between auxiliary contacts 27 and 28 and the arcuate movable contact 25. The auxiliary contacts 27 and 28, so connected to the arcuate contact 25 through the resistors 29, shunt the load current to the succeeding stationary contact to maintain circuit continuity during tap changing, and the resistors 29 limit the circulating current during the interval that the succeeding and preceding winding taps are bridged and reduce the arcing during the tap change.

The taps 20, 21 and 22 on winding section 16 may be connected to even-numbered stationary contacts 6, 4 and 2 respectively of tap changer 24, and the taps 20, 21 and 22 on winding section 17 may be connected to the oddnumbered stationary contacts 1, 3 and 5 respectively.

A double pole, triple throw switch 33 disposed within casing 12 may be actuated by suitable operating means 34 extending through a wall of the casing 12 and having a handle 36 accessible exterior of the casing 12, one suitable means for operating such an internally positioned switch from the exterior of the casing being disclosed in FIG. 19 of the aforementioned Schindler patent. The two poles 37 and 38 of switch 33 are ganged, and the three stationary contacts A, B and C of switch 33 which pole 37 is adapted to selectively engage are individually connected electrically to the taps 20, 21 and 22 respectively of winding section 16, and the three stationary contacts A, B and C of switch 33 which pole 38 is adapted to selectively engage are individually connected electrically to the taps 22, 21 and 20 respectively of winding section 17. One end of each of the primary winding sections 14 and 15 is connected to a primary insulating bushing 48 on casing 12, and the other ends of primary winding sections 14 and 15 are respectively connected to the poles 37 and 38. In this embodiment switch 33 selectively connects the fifty percent winding sections 14 and 15 respectively to the taps 20, 21 and 22 on the five percent winding sections 16 and 17 in order to vary the transformation ratio and thus change the voltage range over which tap changer 24 operates. Table 1 indicates the percent of the rated primary winding 10 in the circuit for each position of tap changer 24 and double pole, triple throw switch 33:

TABLE 1 Switch Position Tap Changer Bridges Contacts Percent Percent Percent Now assume switch 33 is in position C and tap changer arcuate contact 25 bridges stationary contacts 4 and 5. This circuit may be traced from one bushing 48, winding section 14, pole 37, switch stationary contact C, tap 22 on winding section 16, the portion of winding section 16 between taps 22 and 21, tap 21 on winding section 16, tap changer stationary contact 4, arcuate contact 25, stationary contact 5, tap 22 on winding section 17, the portion of winding section 17 between taps 22 and 20, switch stationary contact C, pole 38, and winding section to the other bushing 48. In this position of switch 33 and tap changer 24, the portions of winding sections 16 and 17 between taps 2221 and 2220, respectively, buck the fifty percent winding sections 14 and 15 and only 92 /2 percent of the primary winding is in use.

Table 2 shows the portion of each of the tapped winding sections 16 and 17 which are in the primary winding circuit and the bucking or boosting condition thereof for each position of switch 33 and each position of the tap changer 24 (it should be noted that the winding portions are in boosting relation to the untapped fifty percent sections 14 and 15 when the smaller tap number precedes the larger tap number, e.g., -22, and in bucking relation therewith when the larger tap number precedes the smaller tap number, e.g., 22-20):

TABLE 2 Tap Changer Bridges Contacts Switch Position Pole 37 Connected to Tap Portion of Winding 16 in Circuit Portion of Winding 17 in Circuit Percent Primary Winding Pole 38 Connected to Tap 20-22 21-22 None 20-22 21-22 None 20-21 None 22-21 20-21 None 22-21 None 21-20 2220 can be in a direction to cause each tap section to buck Tap changer 24 may be operated to maintain constant or to boost the fifty percent winding sections 14 and 15. potential on secondary winding 13 by voltage sensitive Circuits will now be traced for representative positions of switch 33 and tap changer 24. Assume switch 33 is in position A and tap changer arcuate contact 25 bridges stationary contacts 2 and 3. The circuit may be traced from one bushing 48, winding section 14, pole 37, switch stationary contact A, tap 20 of winding section 14, winding section 16 to tap 22 thereof, tap changer stationary contact 2, arcuate contact 25, stationary contact 3, tap 21 on winding section 17, the portion of winding section 17 between taps 21 and 22, stationary contact A of switch 33, pole 38, and winding section 15 to the other bushing 48. In this position, the portions of winding sections 16 and 17 between taps 20-22 and between taps 21-22 respectively are both additive to the fifty percent winding sections 14 and 15, and 107 /2 percent of the primary winding is being used.

Assume switch 33 is in position B and tap changer arcuate contact 25 bridges stationary contacts 4 and 5. This circuit may be traced from one bushing 48, winding section 14, pole 37, switch stationary contact B, tap changer stationary contact 4, arcuate contact 25, stationary contact 5, tap 22 on winding section 17, the portion of winding section 17 between taps 22 and 21, tap 21 on winding section 17, switch stationary contact B, pole 38, and winding section 15 to the other bushing 48. Here the current flow in the 2% percent voltage portion of winding section 17 between taps 22 and 21 is in a direction to buck fifty percent winding sections 14 and 15 with the result that only 97 /2 percent of the primary winding turns are, in effect, active.

actuating means 50 which may be of the vibratory electromagnetic pump and Work cylinder type disclosed in the aforementioned Schindler patent or may be of the electronic sensing and shaded pole motor type disclosed in the aforementioned Riebs et al. patent, and tap changer actuating means 50 may sense the transformer secondary voltage and also derive operating energy for the vibratory pump, or the shaded pole motor, over the leads 51 connected across secondary winding 13. Inasmuch as the voltage sensing and tap changer actuating means 50 constitutes no part of the present invention, such means 50 is shown in block form in the drawing in order to simplify the invention and to facilitate the understanding thereof.

FIG. 2 illustrates an embodiment of the invention wherein a single three-position rotary switch means 52 (substituted for the double pole, triple throw switch 33 of the transformer of FIG. 1) disposed within casing 12 changes the effective number of turns in the transformer primary winding 10 in order to vary the range of voltage over which tap changer 24 operates. Switch means 52 includes a first set of stationary contacts W, X, Y and Z and a second set of stationary contacts W, X, Y and Z arranged in spaced apart relation in a circle and also includes a rotatable member 53 carrying two diametrically opposed arcuate metallic contacts (or poles 37 and 38' which are respectively adapted to sequentially bridge between adjacent stationary switch contacts W, X, Y, Z and W, X, Y, Z of the first and second sets. Stationary contacts W and Y are connected to taps 22 and 20 respectively on winding section 16; stationary contacts X and Z are connected to taps 20 and 22 respectively on winding section 17. Switch stationary contacts X and Z are commoned and connected to one end of winding section 14; switch stationary contacts W and Y are commoned and connected to one end of fifty percent winding section 15. Switch means 52 may be actuated by operating means 34 extending through a Wall of casing 12 so that arcuate contacts 37 and 38' connect winding sections 14 and 15 individually to taps 20 and 22 of winding sections 16 and 17 respectively in order to vary the effective number of 5 former primary voltage when it is connected in the circuit by switch 60. End tap 66 of winding section 15 is connected to a bushing 48 in a manner similar to the FIG. 1 embodiment.

Switch 60 is adapted to be actuated by operating means 34 which extend through a Wall of casing 12 and is accessible from the exterior of casing 12. In switch position A, arcuate contact 37' commons stationary contacts Y and Z to connect the entire winding section 15 to tap 22 on winding section 17. In position B contact 37 bridges stationary turns of pnmary wlpdmg thus change the Zi contacts X and Y to connect the end tap 64 to tap 20 on of voltages 0Ve.r Whlch a g i fi i winding section 17. In position C arcuate contact 37 i fifd ii 55132131513; iiniafy il'iiial firfii 2 53112 bridges Stationery contacts W and X to disconnect nnn bucking and boosting condition thereof for each tap tap 64 windmg F 15 and to connect P to P changer position and each of the Switch Positions A, B on winding section 17. Table 4 shows the portions of and C wherein the arcuate contact 37 respectively bridges the iaPl?ed W1nd1ngS P 17 m h transfprmer P the Switch Stationary contacts and and mary wmdmg and the bucking or boosting relation thereof arcuate contact 38' bridges switch stationary contacts for 9 PQSIUOH of p changer 24 f 0f SWltCh and XLY, and WLX', and it Should be noted h 20 again 1t should be noted that the particular winding portion the Winding portions are in boosting relation where the is in bucking relation when the larger tap number precedes smaller tap number comes before the larger tap number, the lower tap number, 1.e., 22-20 designates that the winde.g., 20-22, and in bucking relation when the larger tap ing portion between taps 20 and 22 is in bucking relation number precedes the smaller tap number, e.g., 22-20: to the WlIlCllIlg sections 14 and 15.

TABLE 3 W d W dn Portion of Portion of Percent hiiti g Switch 14 :351 lfi flo n- Winding 16 Win i i11g 17 Primary Contacts Position nected nected in Circuit in Circuit Wmdmg to Tap to Tap 22 20-22 20-22 110 h 20 20-22 None 105 O 22 20 None None 100 A 20 22 20-22 21-22 107 B 20 20 20-22 21-20 102 0 22 20 None 21-20 97 A 20 22 20-21 21-22 105 B 20 20 20-21 21-20 100 0 22 20 22-21 21-20 95 A 20 22 20-21 None 102% B 20 20 20-21 22-20 97% o 22 20 22-21 22-20 92% A 20 22 None None 100 B 20 20 None 22-20 95 O 22 20 22-20 22-20 90 FIG. 3 illustrates an embodiment of the invention TABLE 4 wherein a three position, single pole rotary switch (substituted for the double pole switch 33 of the FIG. 1 Tap Chan er 8 m1 Portion ofWindlng in Circuit P f rterlit W1 embodiment) disposed withm casing 12 changes the num- Bridges Conflicts Position i a ber of effective turns in primary winding 10 in order to 16 17 15 wmdmg vary the range of voltages over which tap changer 24 A 20 22 20 22 64.66 operates. This embodiment utilizes a single tap inter- B 2H2 None 6M6 it? mediate the ends of fifty percent winding section 15, and g 3%; None 65-66 0 21-22 64-66 107% consequently this embodiment 1s more suitable for shell B 20-22 21-20 64-66 102 type transformers than for core type transformers because 2 38:3? gtgg 22:28 35% of the non-symmetrical tap arrangement. Fifty percent 16 58 3} 3:38 g gg 89 winding section 14 is continuous with tapped five percent Winding section 16. 0 20-21 22:20 65-66 93% Switch 60 has four stationary contacts W, X, Y, Z 1 1 0 3:22 1 6 spaced apart in a circle and a rotatable member 53 carry- C None 2H0 65436 3 ing an arcuate metallic contact 37' adapted to sequentially bridge between adjacent pairs of the stationary contacts W, X, Y, Z. Switch stationary contacts X and Z are connected to taps 20 and 22 respectively of winding section 17. Switch stationary contact Y is connected to end tap 64 on fifty percent winding section 15, and switch stationary contact W. is connected to tap 65 on winding section 15. The portion of winding section 15 between taps 64 and 65 preferably generates five percent of the transstationary contacts in the same manner as in the FIG. 3 embodiment. Winding section 17 is continuous with a twenty five percent winding section 68 having an end tap 70 connected to switch stationary contact Z and a tap 69 connected to switch stationary contact X, and the portion of winding section 68 between taps 69 and 70 preferably generates five percent of the transformer primary voltage. The embodiment of FIG. 4 is also more suitable for shell type transformers than for core type transformers because of the non-symmetrical tap arrangement. In switch position A acuate contact 37' bridges stationary contacts Y and Z to connect end tap 70 on winding section 68 to end tap 64 on winding section 15. In switch position B arcuate contact 37 bridges stationary contacts X and Y to connect tap 69 on winding 68 to end tap 64 on winding 15 and thus remove the portion of winding section 68 between taps 69 and 70 from the circuit. In switch position C contact 37' bridges stationary contacts W and X to connect tap 69 to tap 65 on winding section 15 and thus remove from the circuit the portions of winding sections 68 and 15 respectively between taps 69 and 70 and between taps 64 and 65.

Table 5 shows the condition of the five percent voltage portions 6940 and 64-65 of winding sections 68 and respectively for the three switch positions when tap changer arcuate contact 25 bridges tap changer stationary contacts 1 and 2:

FIG. 5 illustrates an embodiment of the invention utilizing a double pole, three position switch 52 similar to the FIG. 2 embodiment but wherein tap sections are removed from the primary winding circuit rather than being connected in bucking relation. Winding sections 14 and 15 are continuous with winding sections 16 and 17 respectively, and additional five percent winding sections 71 and 72 are continuous with the winding sections 14 and 15 respectively. Tap 73 at the junction of winding sections 14 and 71 is connected to switch stationary contact X; tap 74 at the junction of winding sections 15 and 72 is connected to switch stationary contact W. End taps 76 and 77 on winding sections 71 and 72 are respectively connected to stationary contacts Z and Y. Switch stationary contacts W and Y are commoned and connected to one primary bushing 48, and switch stationary contacts X and Z are commoned and connected to the other primary bushing 48. In switch position A arcuate contacts 37 and 38 carried by rotatable member 53 bridge stationary contacts YZ and YZ respectively to connect the primary bushings 48 individually to end taps 76 and 77 and thus insert winding sections 71 and 72 in series with winding sections 14 and 15 respectively. In switch position B contacts 37' and 38 bridge stationary contacts X-Y and XY respectively to connect one bushing 48 (shown on the left in FIG. 5) to tap 73, and thus remove winding section 71 from the primary winding circuit, and to connect the other primary bushing 48 to end tap 77 so that winding section 72 remains active. In switch position C arcuate "contacts 37' and 38' bridge contacts W-X and W'X respectively to connect the bushings 48 directly to taps 73 and 74 and thus remove both winding sections 71 and 72 from the circuit.

Table 6 shows the condition of the two five percent winding sections 71 and 72 for the three switch positions when tap changer arcuate contact 25 bridges tap changer stationary contacts 1 and 2;

TABLE 6 Percent Tap Changer Switch Winding Winding I ota1 Bridges Contacts Position Section 71 Section 72 Primary Winding A In circuit In circuit 110 B Out of circuit. .....(10 105 C do Out of circuit While only a few embodiments of the invention and of the switch means for varying the voltage range over which the tap changer operates have been illustrated and described, many modifications and variations thereof will be readily apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention:

I claim:

1. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having separate first and second winding sections each of which is provided with taps and having approximately equal number of turns between adjacent taps, a tap changer within said casing having a plurality of stationary contacts and odd-numbered stationary contacts thereof being connected to the taps of said first winding section and evennumbered stationary contacts thereof being connected to the taps of said second winding section, said tap changer also having a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, means including a multi-position switch within said casing for varying the transformation ratio of said transformer in a plurality of steps, whereby the voltage range over which said tap changer operates may be varied, and means extending through a wall of said casing and being accessible from the exterior of said casing for selectively actuating said switch between positions.

2. In the combination defined by claim 1 wherein said primary winding has a separate third winding section and said switch connects said third winding section to different taps on one of said first and second winding sections in order to vary the voltage range over which said tap changer operates.

3. In the combination defined by claim 1 wherein said primary winding also has separate third and fourth sections and said switch has a pair of movable contacts adapted to connect said third and fourth winding sections to different taps on said first and second winding sections respectively to vary the voltage range over which said tap changer operates.

4. In the combination defined by claim 3 wherein said switch has first and second sets of stationary contacts and certain contacts of said first and second sets are individually connected to taps on said first and second winding sections respectively and other stationary contacts thereof are connected to said third and fourth winding sections respectively and said switch also has a rotatable member carrying a pair of elongated metallic contacts each of which is adapted to sequentially bridge between adjacent stationary contacts of one of said sets to vary the voltage range over which said tap changer operates.

5. In the combination defined by claim 3 wherein said switch has first and second sets of stationary contacts individually connected to said taps on said first and second winding sections respectively and also has ganged first and second poles selectively operable into engagement with the stationary contacts of said first and second sets of stationary switch contacts respectively and being electrically connected to said third and fourth winding sections respectively.

6. In the combination defined by claim 1 wherein said primary winding has additional taps and said switch has stationary contacts connected to said additional taps and operates.

7. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having separate first and second winding sections each of which is provided with taps and having approximately equal number of turns between adjacent taps, a tap changer within said casing having a plurality of stationary contacts and odd-numbered stationary contacts thereof being connected to the taps of said first winding section and evennumbered stationary contacts thereof being connected to the taps of said second winding section, said tap changer also having a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, said primary winding also having separate third and fourth untapped winding sections, a multi-position switch within said casing having first and second sets of spaced apart stationary contacts with odd-numbered stationary contacts of said first set connected to individual taps on said first winding section and even-numbered contacts of said first set commoned and connected to said third winding section, even-numbered stationary contacts of said second set being connected to individual taps on said second winding section and odd-numbered contacts of said second set being commoned and connected to said fourth winning section, said switch also having a pair of movable metallic contacts each of which is adapted to bridge between adjacent stationary contacts of one of said sets, and means extending through a wall of said casing and being accessible from the exterior of said casing for selectively operating said switch between positions.

8. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having separate first and second winding sections each of which is provided with taps and having approximately equal number of turns between adjacent taps, a tap changer within said casing having a plurality of stationary contacts and odd-numbered stationary contacts thereof being connected to the taps of said first winding section and even-numbered stationary contacts thereof being connected to the taps of said second winding section, said tap changer also having a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, said primary winding also having additional taps, multi-position switch means within said casing for connecting and disconnecting the portion of said primary winding between said additional taps to vary the voltage range over which said tap changer operates, and means extending through a wall of said casing and being accessible from the exterior of said casing for selectively operating said switch means between positions, whereby the voltage range over which said tap changer operates may be varied without opening said casing.

9. In the combination defined by claim 8 wherein said primary winding has a separate third winding section and said additional taps are in said third winding section and said switch means selectively connects said additional taps to one of said first and second winding sections.

10. In the combination defined by claim 9 wherein said switch means selectively connects said additional taps to different individual taps on one of said first and second winding sections.

11. In the combination defined by claim 9 wherein said switch means includes a plurality of stationary contacts with odd-numbered stationary contacts connected to said additional taps and even-numbered contacts connected to individual taps on one of said first and second winding sections and said switch means also includes a movable metallic contact adapted to sequentially bridge between adjacent pairs of said stationary switch contacts.

12. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having separate first and second Winding sections each of which is provided with a plurality of taps adjacent one end thereof and having an approximately equal number of turns between adjacent taps, a tap changer within said casing having a plurality of stationary contacts with odd-numbered stationary contacts connected to the taps of said first winding section and even-numbered stationary contacts connected to the taps of said second winding section, said tap changer also having a movable metallic contact adapted to sequentially common adjacent pairs of said stationary contacts, said first and second winding sections also h ving an additional tap adjacent the other end thereof, a single switch means within said casing for selectively connecting to and disconnecting from said primary winding the portions of said first and second winding sections disposed between said other end and said additional tap, and means extending through a wall of said casing and being accessible from the exterior of said casing for operating said switch means.

13. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having separate first and second winding sections each of which is provided with a plurality of taps, a tap changer within said casing having a plurality of stationary contacts with odd-numbered stationary contacts connected to the tap on said first winding section and even-numbered stationary contacts connected to the taps on said second winding section, said tap changer also having a movable metallic contact adapted to sequentially common adjacent pairs of said stationary contacts, third and fourth winding sections Within said casing, a single switch means within said casing for selectively connecting said third and fourth winding sections in series with said first and second winding sections respectively, and means extending through a wall of said casing and being accessible from the exterior of said casing for operating said switch means, whereby the voltage range over which said tap changer operates can be varied without opening said casing.

14. In the combination defined by claim 13 wherein said switch means has first and second sets of stationary contacts and a rotatable member carrying a pair of elongated metallic contacts each of which is adapted to bridge between stationary contacts of one of said sets when said member is turned and wherein the ends of said third winding section are connected to alternate stationary contacts of said first set and the ends of said fourth winding section are connected to alternate stationary contacts of said second set.

15. An electrical transformer having a pair of inductively related windings, one of said windings having separate first and second winding sections each of which is provided with a plurality of taps and having approximately equal number of turns between adjacent taps, a tap changer having a plurality of stationary contacts and odd-numbered stationary contacts thereof being connected to the taps of said first winding section and even-numbered stationary contacts thereof being connected to the taps on said second winding section, said tap changer also having a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, whereby said tap changer can vary the voltage ratio of said transformer in steps, and means including a multi-position switch for varying the number of effective turns of one of said pairs of windings in a plurality of steps, whereby the voltage range over which said tap changer operates may be changed.

16. An electrical transformer having a pair of inductively related windings, one of said windings having four separate winding sections the first and second of which are provided with taps, a tap changer having a plurality of stationary contacts with odd-numbered stationary contacts connected to the taps of said first winding section and even-numbered stationary contacts connected to the tap of said second winding section and a movable Contact adapted to sequentially common adjacent pairs of said stationary contacts, and switch means for selectively connecting said third and fourth winding sections respectively to said taps on said first and second winding sections, whereby the voltage range over which said tap changer operates may be varied.

17. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, said primary winding having four separate winding sections the first and second of which are provided with taps, a tap changer within said casing having a plurality of stationary contacts and movable contact adapted to sequentially common adjacent pairs of said stationary contacts, even-numbered stationary contacts being connected to the taps on said first winding section and odd-numbered stationary contacts being connected to said taps on said second winding section, and a double pole, triple-throw electrical switch within said casing, the poles of said switch being individually connected to said third and fourth winding sections and the stationary switch contacts associated with each of said poles being individually connected respectively to said taps on said first and second winding sections, and means extending through a wall of said casing and being accessible from the exterior of said casing for operating said double pole switch.

18. In combination, an electrical transformer having a casing, inductively related primary and secondary windings within said casing, one of said windings having four separate sections the first and second of which are provided with taps, a tap changer within said casing having a plurality of stationary contacts and a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, the taps of said first section being connected to even-numbered stationary contacts of said tap changer and the taps of said second section being connected to odd-numbered stationary contacts thereof, switch means within said casing for selectively connecting said third and said fourth sections respectively to said taps on said first and second sections, and means extending through a wall of said casing and being accessible from the exterior of said casing for operating said switch means, whereby the voltage range of said tap changer may be changed from the exterior of said casing.

19. In combination, an electrical transformer having a casing, a core and coil assembly including inductively related primary and secondary windings within said casing, said primary winding having four separate Winding sections the first and second of which are provided with taps, a tap changer within said casing having a plurality of stationary contacts and a movable contact adapted to sequentially common adjacent pairs of said stationary contacts, even-numbered stationary contacts being connected to the taps on said first Winding section and oddnumbered stationary contacts being connected to said taps on said second winding section, voltage sensitive means coupled to said secondary winding for actuating said tap changer movable contact in a direction to maintain substantially constant voltage on said secondary winding, a double pole, triple-throw switch Within said casing having the poles thereof individually connected to said third and fourth winding sections and the stationary contacts associated with each of said poles individually connected respectively to said taps on said first and second winding sections, and means extending through a wall of said casing and being accessible for the exterior of said casing for operating said switch, whereby the voltage range over which said tap change-r operates may be varied without opening said casing.

References Cited UNITED STATES PATENTS 2,200,979 5/1940 Blume 32343.5 3,167,703 l/l965 Schindler 32343.5 3,172,030 3/1965 Farry 323-45 JOHN F. COUCH, Primary Examiner.

W. E. RAY, Assistant Examiner. 

16. AN ELECTRICAL TRANSFORMER HAVING A PAIR OF INDUCTIVELY RELATED WINDINGS, ONE OF SAID WINDINGS HAVING FOUR SEPARATE WINDING SECTIONS THE FIRST AND SECOND OF WHICH ARE PROVIDED WITH TAPS, A TAP CHANGER HAVING A PLURALITY OF STATIONARY CONTACTS WITH ODD-NUMBERED STATIONARY CONTACTS CONNECTED TO THE TAPS OF SAID FIRST WINDING SECTION AND EVEN-NUMBERED STATIONARY CONTACTS CONNECTED TO THE TAPS OF SAID SECOND WINDING SECTION AND A MOVABLE CONTACT ADAPTED TO SEQUENTIALLY COMMON ADJACENT PAIRS OF SAID STATIONARY CONTACTS, AND SWITCH MEANS FOR SELECTIVELY CONNECTING SAID THIRD AND FOURTH WINDING SECTIONS RESPECTIVELY TO SAID TAPS ON SAID FIRST AND SECOND WINDING SECTIONS, WHEREBY THE VOLTAGE RANGE OVER WHICH SAID TAP CHANGER OPERATES MAY BY VARIED. 